Several instruments have been developed to collect data resulting from machining operations performed by brake lathes. For example, determining the separation of tool bits of the lathe, and hence the thickness of the brake disk that will result from machining the brake disk with the tool bits in their current positions, is taught for on-vehicle brake lathes in U.S. Pat. No. 6,363,821, and for bench lathes in U.S. Pat. No. 5,765,457. Both of these patents teach comparison of the indicated thickness to a selected manufacturer specification for minimum thickness to provide the lathe operator a warning of when the thickness is not large enough to meet the specification, in which case the disk should be replaced rather than resurfaced.
Another example of instrumentation to provide information on a lathe operation is taught in U.S. Publication 2009/0107309, which teaches an alignment monitor for a hub-mounted lathe that provides a real-time indication of the misalignment between an axis of the lathe and an axis of rotation of the disk as the alignment is dynamically adjusted. A comparison to a selected alignment specification can be provided to allow the lathe operator to stop the adjustment manually when the misalignment is small enough to meet the specification.
While such instruments can provide the lathe operator information regarding the current stage of the resurfacing procedure, they do not provide guidance for inexperienced lathe operators, and do not provide records of the machining operations performed by the lathe.
Instrumentation for determining when a cut is complete have been suggested. One patent that addresses completion of a cutting operation on a brake disk is U.S. Pat. No. 6,729,212, which teaches an iterative method for machining a brake disk while monitoring contact of the tool bits with the disk surfaces using electrical conductivity sensors. The method taught in the '212 patent requires multiple passes of the tool bits over the disk surface, with the depth of cut increased for each subsequent pass. This process is continued until such time as the electrical signal indicates substantially continuous contact throughout the pass, at which time the cutting operation is considered complete. This method appears to be extremely time consuming.
Another approach is taught in U.S. Pat. No. 7,640,832, which teaches monitoring either electrical contact signals or vibration signals to provide an operator with a visual and/or audio notice of when the tool bits of an on-vehicle brake lathe are in contact with the disk surfaces. The '832 patent teaches that, when such contact is lost, indicating the end of a cut, the motor of the lathe can be shut off to minimize delay before a subsequent machining operation can be conducted.
A limitation of both of the '212 and the '832 approaches is that they rely on instantaneous signals for contact, and thus may be susceptible to false indications of whether the cut is completed when the disk surfaces are irregular.